My question is- am I sacrificing anything (performance...) by using a string of this size.
Very little by way of performance...probably 2-4 fps., possibly a little more but not likely.
Talk to the folks at BW about Ken Beck's string challenge. Some bows may show a larger margin with a smaller string. I haven't experienced it personally. I have talked to shooters who feel they loose stability by going too small.
My experience with the BW "factory" strings is they don't pad the loops, and aren't as quiet as they could be. I think they are machine-made, which doesn't lend itself to padding the loops? The guys at BW could answer that question.
I have made strings for BW bows at my shop and never had to do to extremes to get them very quiet. The "factory" strings are 14 strands of Dynaflight '97 (if it hasn't changed). I generally use 12 (Dynafligh '97 or 8125G), with the loops padded to 18. My bet is 16-18 strands of 8190 with padded loops would also work well. Of course you have to do your part with tuning and silencer placement.
Chad